Different types of non-destructive measuring system are known that are adapted to the natures of different types of object, however each system is often specific, either as to the type of measurement that is desired or else to the type of object that is under consideration.
Destructive measurement systems are set aside and are not considered in the present invention since one of the objects of the invention is to be able to determine the characteristics of objects for the purpose of sorting them: since destructive measurements can naturally only be performed on samples, they cannot achieve this object.
For measuring dimensions, mention may be made of various means, essentially such as those that make use of optical sensors: specific examples include firstly French patent 1 458 715 filed by the firm Fairbanks Morse on Oct. 7, 1965 claiming US priority and describing a frame having a light grid through which each object passes, thereby intersecting the beams and obscuring cells situated on the axis of the beams, and secondly PCT application WO 90/04803 filed Sep. 28, 1990 by the Australian firm Colour Vision Systems Ltd., describing a device including an array camera and an image analyzer.
For measuring the firmness of objects, numerous sensors are known that serve, in fact, to measure the hardness of the objects, essentially by measuring a displacement or a deformation of a known surface subjected to a given force: when the object is fragile, none of these sensors can be used directly because of the risk of damaging the object.
In the main application of the present invention, mention may be made, by way of example, of three systems adapted to fruit:
An article by Mr. John S. Perry published in "Transactions of the ASAE" (American Society of Agricultural Engineers), 1977, 20/4, pp. 762-767, which teaches a device into which air is delivered at a given pressure and a deformation is measured. That device is nevertheless unsuitable for in-line measurements since the method takes time and requires very good contact between the instrument and the fruit. If it is desired to perform measurements on a line operating at a high rate, there is a risk of the objects rubbing against the surfaces subjected to pressure, thereby damaging the surfaces of said objects.
An article by J. J. Mehlschau et al. in another "Transactions of the ASAE", 1981, 24.05, pp. 1368-1375, teaches an in-line sensor for pears, the sensor including horizontal wheels applied laterally against the pears as they go past, which wheels are subjected to a given force. The problem with that system is the residual bruising that remains after the measurement and which has the appearance of a rail in fruit that is rather ripe.
An article by J. E. Mattus described in a publication of the "American Society for Horticultural Science", 1967, Vol. 87, pp. 100-103, teaches a "mechanical thumb" based on the principle of a penetration meter having a tip that is smaller than the tips used in destructive testing. That system requires a measurement time that is quite long since the fruit must initially be pressed against a hard surface and then the sensor must be applied at right angles which means that the measurement cannot be performed in real time on a line, at least not without accepting a loss of reliability in the measurement and an increase in the risk of damage by contact with the surface of the object.
The first two systems described above may also be used for measuring the diameters of fruit. Other systems may also be mentioned using other means for measuring ripeness and/or firmness, e.g. by vibration and propagation of sound, or by analyzing the way light is transmitted and/or absorbed, or on the basis of the overall color of the fruit, but the results are not very accurate and do not enable reliable and repetitive measurements to be performed to enable sorting to be performed continuously with better than 80% good results, and that is one of the essential objects of the present invention.
It may be mentioned that numerous equipments, tests, and publications have been, and are still being, developed for determining a criterion of fruit ripeness. Patent applications have been made in respect of some of them, essentially for automatically measuring firmness which is the factor most representative of ripeness, and for the purpose of replacing human judgement which is tedious, subject to error, and expensive.
Commercially, fruit are sorted on the basis of firmness firstly to separate out the ripest and thus the best fruit from the others, thereby sorting for eating quality, and also for separating out fruit more capable of withstanding a long journey from the others, which in the end amounts to sorting for appearance. For example, overripe peaches that have travelled over a long distance do not look inviting on arrival.
For a long time, firmness has been out of favor for in-line applications since the method conventionally used, such as the Magness-Taylor penetration meter, is destructive. It has therefore appeared that a method taking this parameter into account could only be destructive. For measuring dimensions, optical methods have generally been preferred in research, but without achieving results of satisfactory reliability.
Thus, against the usage and practice currently recommended in the profession, the present invention is the result of studies and research on measuring the firmness criterion to enable sorting for two purposes, not only for eating quality, but also for appearance. This criterion appears to be highly pertinent since it makes it possible:
to separate fruit into different classes of eating quality, thus making it possible to offer a "reliable" product to customers;
to make up trays of fruit having uniform firmness, with the harder fruit being suitable for shipping over longer distances; and
in the long term, to pay producers as a function of the quality of their fruit, thereby increasing quality levels overall.
None of the presently-available systems, some of which are mentioned above, is capable of measuring this criterion with sufficient reliability while satisfying the objects of the present invention.
In general terms, the problem posed is that of providing apparatus for performing non-destructive measurements of characteristics, such as firmness, but also dimensions, on fragile objects such as fruit of non-uniform sizes while they are being continuously transported by a conveyor system, and for the purpose of being sorted as a function of the results of said measurements so as to be delivered one by one to various outlets each corresponding to criteria for given categories, with the selection success rate being greater than 80% and without significantly damaging or visually marking the surface of the fruit.